Forage frost protection potential of conifer silvopastures

https://doi.org/10.1016/S0168-1923(02)00058-8Get rights and content

Abstract

In temperate climates, forages are frequently held in a near dormant state at both ends of the growing season due to episodic radiation frost. During these periods, air temperature is frequently adequate for forage growth to supply feed for grazing animals. The effect of thermal radiation from conifer tree canopies on forage canopy temperature was evaluated for a silvopasture with variable tree density. A long-wave radiation-sensitive sensor for measuring temperature at the forage canopy level was designed, tested, and used to approximate night time forage canopy temperature during the autumn of 1999 and 2000 and spring of 2000. Temperature from the designed sensor correlated linearly with forage canopy temperature measured with an infrared thermometer with a slope of 1.0, a 0.9 °C offset, and an r2 of 0.999. The response of sensor temperature to night sky shading by trees was also linear. Under 77% tree cover sensor temperature remained within half a degree of air temperature, however, under 7% cover averaged 10.4 °C below air temperature during radiation frost events. The results of this study indicate that a well designed silvopasture can potentially extend the grazing season period on both ends in regions were radiation frosts are prevalent.

Introduction

Agricultural production in temperate climate areas is constrained by cold weather which limits the growing season. Radiation frosts frequently injure vegetation early and late in the growing season even when air temperature is warm enough to maintain plant health. Radiation frost occurs at night when clear sky conditions result in a large net loss in long-wave radiation from plant surfaces and a lack of wind minimizes convective heat gain from air.

Obstructing the open sky from a plant’s upward field-of-view is one strategy for reducing the severity of radiation frost by providing a surface much warmer than open sky with which plants exchange long-wave radiation. Shade cloth mounted over vegetation is effective for reducing radiation frost, however, the cost limits its use to protection of high value products (Stamps, 1989, Igarashi et al., 1993, Teitel et al., 1996, Scowcroft et al., 2000).

Trees can provide an economical interface between crops and open sky that minimizes damage from radiation frost. Overstory trees are effectively used to prevent frost damage on coffee crops south of 20° latitude in South America (Caramori et al., 1996). In northern Europe, birch shelterwoods provide conifer saplings with some frost protection (Odin et al., 1984). While an analysis of tree overstory benefits on forage production has not been made, there have been observations of improved forage growth under conifer trees during cold weather (Sibbald et al., 1991, Brazoptos and Papanastasis, 1995).

The objective of this project is to quantify the relationship between tree canopy density in a conifer silvopasture and the severity of radiation frost.

Section snippets

Theoretical consideration

Net radiation, which is a major driver of plant climate, is most simply defined byRn=Ri−Rowhere Ri (W m−2) is incoming radiation and Ro (W m−2) is outgoing radiation. During the daytime, both of these components contain short-wave and long-wave radiation. At night, however, the short-wave components are equal to zero.

The outgoing long-wave radiation from a surface is defined by the Stefan–Boltzmann equation asRo=σεT4where σ is the Stefan–Boltzmann constant (5.6697×10−8 W m−2 K−4), ε the thermal

Materials and methods

The research site is a 0.7 ha area of 35-year-old, 17 m tall, mixed conifers on a farm site in southern West Virginia (37°46′W latitude 81°00′N longitude 860 m elevation). The site is dominated by white pine (Pinus strobus L.) and red spruce (Picea rubens Sarg.) with a few scattered pitch pine (Pinus rigida Mill.) and short-leaf pine (Pinus echinata Mill.). The trees are growing on a Gilpin soil (fine loamy, mixed, mesic Typic Hapludult). The understory vegetation is dominated by orchardgrass (

Results and discussion

The tree canopy cover ratios (mt), determined using the WinSCANOPY software, for the sky field-of-view at the eight silvopasture sensor sites were 0.77, 0.77, 0.75, 0.74, 0.70, 0.65, 0.60, and 0.55. These values represent the range of tree canopy cover within the conifer stand. The mt value for the adjacent field site without trees was 0.07 rather than 0 due to distant horizon obstruction.

The RFP sensors gave temperature values highly correlated with actual grass canopy temperature measured

Conclusions

A considerable amount of silvopastoral research has been focused on the impact of shade on forage accumulation and quality (Kephart and Buxton, 1993, Devkota et al., 1997, Lin et al., 1999). However, forages may be adversely impacted by radiation frosts early and late in the growing season. The ability of silvopastures to extend the growing season during these periods as a result of trees protecting forages from radiation cooling, to which open pastures are subjected, appears to be substantial.

Acknowledgements

I thank Barry L. Harter for the excellent technical assistance in carrying out this research and for design improvements suggested for the RFP sensor.

References (17)

There are more references available in the full text version of this article.

Cited by (19)

  • Opportunities and challenges for the integration of sheep and crops in the Rio de la Plata region of South America

    2022, Small Ruminant Research
    Citation Excerpt :

    Fig. 1 shows examples of sheep integration into perennial systems that are practiced in the Rio de la Plata region. In addition, integrated systems of this kind provide thermal comfort to the animals (Vieira Junior et al., 2019), reduce the severity of low temperatures in the pasture by microclimate control (Feldhake, 2002), and contribute to mitigating greenhouse gases emissions (Torres et al., 2017). Thus, integrating sheep and trees constitutes productive diversification and is in line with the logic of sustainable intensification.

  • Silvopasture in the USA: A systematic review of natural resource professional and producer-reported benefits, challenges, and management activities

    2022, Agriculture, Ecosystems and Environment
    Citation Excerpt :

    In addition to livestock benefits, producers have reported integrating silvopasture into grazing systems to enhance forage production and quality (Huntsinger et al., 1997; Mills, 2000; Moseley, 2012; Fike, 2016a; Zamora, 2016; Orefice et al., 2017; Keeley et al., 2019). Because of the partially shaded and modified microclimate, forage production can be enhanced, particularly during the early spring and late fall (Feldhake, 2002) and times of drought (Frost and McDougald, 1989; Kallenbach et al., 2006; Ford et al., 2019b; Alley and Marsh, 2021). A producer in Virginia described being able to produce forage during the coldest and hottest months of the year in the silvopasture, allowing for almost year-long grazing (Frey and Fike, 2018).

  • Temporal, environmental and spatial changes in the effect of windbreaks on pasture microclimate

    2021, Agricultural and Forest Meteorology
    Citation Excerpt :

    The largest magnitude of windbreak effects occurred during summer, although effects persisted throughout the year impacting on critical growing times. For example increased paddock temperatures observed during spring and autumn mornings at 1.5 TH and beyond may lead to increased growing season by protecting paddocks from frosts (Feldhake, 2002) or increasing growing degrees days, resulting in faster crop rotations. Additionally, growing season length may be altered by changes in soil moisture due microclimate changes impacting evapotranspiration.

View all citing articles on Scopus
View full text